This invention pertains to the art of bushings and more particularly to clinch free cam bushings. The invention is particularly applicable to a method of making full round bushings and will be described with particular reference thereto. However, it will be appreciated that the invention has broader applications and may be advantageously employed in other fastening and joining environments and applications requiring close tolerances.
Typically, full round bushings have been produced by one of the following standard methods. According to a first method, a strip of bimetal material is formed into a round, generally cylindrical shape in which opposed edges of the material are joined or interlocked by clinching. The clinched edges resemble the interlocking pattern of a dovetail or cooperating puzzle pieces. Generally, a wide range of bearing metal alloys can be used with an outer steel layer which also makes clinched design bushings attractive from a manufacturing standpoint. Clinched design bushings have met with commercial success when used in high volume since manufacturers have automated machinery for supporting a workpiece during various machining steps. Such a design requires extensive fixturing and precise assembly control. In those applications where fixturing is not readily available, the detailed assembly can pose difficult problems. These manufacturing requirements do not make it economical or practical for low or moderate volume bushing production runs.
Other drawbacks are associated with the clinched design. For example, the clinched seam can become loose or distorted during installation which, in turn, causes the bushing to be out-of-round and unusable for its intended purpose.
A second standard method of producing full round bushings is an enhancement of the first. In this method the strip formed bushing seam is welded using electron beam, T.I.G., M.I.G., submerged arc, or other standard welding processes. The disadvantages of these processes are cost and resultant quality. The electron beam process must be performed in a full or partial vacuum and is therefore slow and costly. The other processes mentioned are of high heat intensity and can damage the structure of low melting point bearing materials and the bonding of these materials to the steel backing.
A third standard method involves the drawing of a full round product from pre-cast, sintered, or clad bimetallic strip. This method is limited by the types of materials that can be drawn, is slow, and inefficient in the use of material and is, therefore, costly.
A final standard method of producing full round bushings involves use of solid tubing having a bearing material cast along the inside diameter thereof. Bushings are then cut to a desired length from the solid tube and, in this manner, there is no visible joint in the steel or bearing material.
Although these bushings do not have the problems associated with the clinch or other designs produced from strip, other problems are associated with this method of manufacture. For example, these bushings are relatively expensive to produce and limited to an inner diameter bearing material that is compatible with centrifugal casting.
It has thus been deemed desirable to produce a full round bushing that may accommodate a large selection of materials for the bearing alloys and yet is relatively inexpensive to manufacture. Further, the distortion and loosening problems associated with the clinch design are preferably to be avoided.